1. Technical Field
The present invention relates to an image forming apparatus equipped with a development device using toner.
2. Related Art
In recent years, an image forming apparatus equipped with a development device using toner has been widely used in home offices and by general users. Functional components and techniques employed in the image forming apparatus used in such environments are desired to adjust to reduction in size and cost and extension in life of the image forming apparatus.
For example, components employed in the image forming apparatus have been reduced in size to adjust to the reduction in the overall size of the image forming apparatus. It is therefore more difficult to install the functional components in the size-reduced image forming apparatus than in a large-sized image forming apparatus.
Further, to adjust to the extension in life of the image forming apparatus, the functional components employed in the image forming apparatus are desired to be as abrasion-resistant as possible over an extended period of time. For example, in the case of a photoconductor serving as a latent image carrier, surface abrasion due to contact with components used in charging, development, transfer, and cleaning processes should be taken into account. To minimize the surface abrasion of the photoconductor, a lubricant applicator for applying a lubricant to the photoconductor may be provided. If the photoconductor is reduced in size to adjust to the reduction in size of the image forming apparatus, however, it is difficult to install the lubricant applicator. Therefore, an external additive containing a lubricant such as silicone oil may be added to the toner to reduce friction on the surface of the photoconductor.
Functional components other than the photoconductor, such as a development roller, have also been extended in life for the life extension of the image forming apparatus. Further, as a recent trend, in an image forming apparatus including a process cartridge housing functional components such as a photoconductor and a development device, the functional components of the process cartridge have been improved in durability to reduce running costs. With the functional components thus improved in durability, the frequency of manual replacement of the process cartridge has been reduced, thereby reducing running costs.
If the toner is stored in the process cartridge in an amount corresponding to the lifespan of the durability-improved functional components, however, the size of the process cartridge is increased, thereby increasing the overall size of the image forming apparatus. According to a recent method, therefore, the process cartridge stores a relatively small amount of toner and is resupplied with toner from a toner cartridge. Accordingly, the process cartridge is not required to be filled at one time with all the toner corresponding to the lifespan of the functional components. If the toner cartridge runs out of toner, the toner cartridge is manually replaced with a new toner cartridge to supply toner. Accordingly, the image forming apparatus is reduced in both size and running cost.
If the toner is added with the above-described external additive containing a lubricant, however, the adhesion of toner particles is increased, thereby reducing the fluidity of the toner. The toner with reduced fluidity accumulates in the development device and continues to be subjected to stress. As a result, the toner is thermally fused and may adhere to functional components contacting the toner. Such toner adhesion occurs prominently when the toner has a relatively small particle diameter or a relatively low glass transition temperature Tg. Particularly in a development device including a regulation member that regulates the thickness of a layer of toner carried on the outer circumferential surface of a development roller serving as a developer carrier, toner with reduced fluidity tends to accumulate in a region in which the thickness of the toner layer is regulated by the regulation member. Moreover, the internal pressure (i.e., powder pressure) is increased in the toner accumulating region. Therefore, the toner tends to adhere to end portions of the regulation member in a width direction perpendicular to the moving direction of the outer circumferential surface of the development roller. The toner thus adhering to the end portions of the regulation member may cause an abnormal image such as a striped image.
If the image forming apparatus uses a process cartridge having a relatively short life, the toner adhesion to the end portions of the regulation member in the development device does not pose a serious issue. However, if the image forming apparatus is equipped with a development device using a regulation member and a development roller improved in durability and supplied with toner from a toner cartridge, the development device is used for an extended period of time. In this case, therefore, the toner adhesion to the end portions of the regulation member is prominent.